From a viewpoint of a reliable design, an optical transmission apparatus (optical transmission system) is often configured so as to contribute to redundancy in a communication line. One of the redundancy scheme in the communication line will be found in the optical unidirectional path switched ring (OUPSR) scheme. Using switching operation by an optical switch or switches mounted in a receiving side of a transponder unit, the OUPSR scheme carries out a redundancy scheme by a wavelength in an interexchange channel. One of the OUPSR schemes is disclosed in Japanese Laid-open Patent Publication 11-17261.